Implantable dual sensor bio-pressure transponder and method of calibration

Abstract

A bio-pressure sensor system is disclosed, comprising a first sensor configured to provide a reference pressure measurement and second sensor configured to measure a fluid pressure within a human body. The bio-pressure sensor system also comprises a first reference element and second reference element. The first and second sensors share the first reference element. The second reference element is coupled to the first sensor and configured to provide a reference pressure. The first and second sensors each comprise independent output signals.

I claim: 
     
       1. A method for calibration of a bio-pressure sensor having a housing implanted in a patient, the bio-pressure sensor comprising a first pressure sensor and a second pressure sensor, the first and second pressure sensors being disposed within the housing of the bio-pressure sensor, the first pressure sensor to measure a fluid pressure associated with a reference fluid, the second pressure sensor to measure a fluid pressure associated with a bodily fluid within a human body, the method comprising:
 receiving a first position pressure measurement signal from a first measurement from the first pressure sensor disposed within the housing with the patient in a first position, the first position pressure measurement signal being based on pressure on the first pressure sensor from the reference fluid and not from the bodily fluid; 
 receiving a second position pressure measurement signal from a second measurement from the first pressure sensor with the patient in a second position, the second position pressure measurement signal being based on pressure on the first pressure sensor from the reference fluid and not from the bodily fluid; 
 receiving a first known reference pressure value of the reference fluid associated with the patient in the first position; 
 receiving a second known reference pressure value of the reference fluid associated with the patient in the second position; 
 calculating a gain correction value based on the first position pressure measurement signal, second position pressure measurement signal, first known reference pressure value, and second known reference pressure value; and 
 correcting a pressure measurement signal from a pressure measurement from the second pressure sensor disposed within the housing with the calculated gain correction value. 
 
     
     
       2. The method of  claim 1 , wherein receiving the first known reference pressure value comprises calculating a first expected position-dependent pressure of the reference fluid disposed in an implanted fluid-filled device with the patient in the first position. 
     
     
       3. The method of  claim 2 , wherein receiving the second known reference pressure value comprises calculating a second expected position-dependent pressure of the reference fluid disposed in the fluid-filled device with the patient in the second position. 
     
     
       4. The method of  claim 2 , wherein the first position is defined as a reference axis extending along a length of the fluid-filled device being at a first angle with a gravitational field acting on the fluid-filled device, and the second position is defined as the reference axis being at a second angle with the gravitational field, wherein the first position and the second position are different. 
     
     
       5. The method of  claim 4 , wherein the first angle is 0°, and calculating the expected pressure of the reference fluid disposed in the fluid-filled device with the fluid-filled device in the first position comprises calculating a product of a density of the reference fluid in the fluid-filled device, gravitational acceleration, and a length of the reference fluid within the fluid-filled device. 
     
     
       6. The method of  claim 1 , further comprising:
 receiving an environmental pressure value derived from the first and/or second measurements; 
 receiving a known environmental pressure value measured by a calibrated device disposed ex-vivo; and 
 calculating an offset correction value based on the environmental pressure value and the known environmental pressure value, 
 wherein correcting the pressure measurement signal from the pressure measurement from the second pressure sensor further comprises correcting the pressure measurement signal from the pressure measurement from the second pressure sensor with the calculated offset correction value. 
 
     
     
       7. The method of  claim 1 , wherein the gain correction value is calculated by dividing a difference in the first position pressure measurement signal and the second position pressure measurement signal by a difference in the first known reference pressure value and the second known reference pressure value. 
     
     
       8. The method of  claim 1 , wherein an amplifier and/or microprocessor corrects the pressure measurement signal from the second pressure sensor. 
     
     
       9. The method of  claim 1 , wherein receiving the second known reference pressure value comprises calculating a second expected position-dependent pressure of the reference fluid disposed in an implanted fluid-filled device with the patient in the second position. 
     
     
       10. The method of  claim 1 , wherein the first and second position pressure measurement signals are voltages corresponding to the first and second pressure measurements acquired by the first pressure sensor with the patient in the first and second positions, respectively. 
     
     
       11. The method of  claim 1 , wherein the first and second known reference pressure values are known pressures. 
     
     
       12. The method of  claim 1 , further comprising correcting a pressure measurement signal from a pressure measurement from the first pressure sensor disposed within the housing with the calculated gain correction value. 
     
     
       13. A method for calibration of a bio-pressure sensor having a housing implanted in a patient, the bio-pressure sensor comprising a first pressure sensor and a second pressure sensor, the first and second pressure sensors being disposed within the housing of the bio-pressure sensor, the first pressure sensor to measure fluid pressure associated with a reference fluid, the second pressure sensor to measure a fluid pressure associated with a bodily fluid within a human body, the method comprising:
 receiving a first position pressure measurement signal derived from a measurement from the first pressure sensor disposed within the housing with the patient in a first position, the first position pressure measurement signal being based on pressure on the first pressure sensor from the reference fluid and not from the bodily fluid; 
 receiving a second position pressure measurement signal derived from a measurement from the first pressure sensor with the patient in a second position, the second position pressure measurement signal being based on pressure on the first pressure sensor from the reference fluid and not from the bodily fluid; 
 receiving a first known reference pressure value of the reference fluid associated with the patient in the first position; 
 receiving a second known reference pressure value of the reference fluid associated with the patient in the second position; 
 calculating a gain correction value based on the first position pressure measurement signal, second position pressure measurement signal, first known reference pressure value, and second known reference pressure value; and 
 correcting, with the calculated gain correction value, a pressure differential measurement value derived from a difference between a pressure measurement signal from a measurement from the second pressure sensor disposed within the housing and a pressure measurement signal from a measurement from the first pressure sensor disposed within the housing, wherein the pressure measurement from the second pressure sensor and the pressure measurement from the first pressure sensor are received simultaneously. 
 
     
     
       14. The method of  claim 13 , wherein receiving the first known reference pressure value comprises calculating a first expected position-dependent pressure of the reference fluid disposed in an implanted fluid-filled device with the patient in the first position. 
     
     
       15. The method of  claim 14 , wherein receiving the second known reference pressure value comprises calculating a second expected position-dependent pressure of the reference fluid disposed in the fluid-filled device with the patient in the second position. 
     
     
       16. The method of  claim 14 , wherein the first position is defined as a reference axis extending along a length of the fluid-filled device being at a first angle with a gravitational field acting on the fluid-filled device, and the second position is defined as the reference axis being at a second angle with the gravitational field, wherein the first position and the second position are different. 
     
     
       17. The method of  claim 13 , further comprising:
 receiving an environmental pressure value derived from the first and/or second measurements; 
 receiving a known environmental pressure value measured by a calibrated device disposed ex-vivo; and 
 calculating an offset correction value based on the environmental pressure value and the known environmental pressure value, 
 wherein correcting the pressure differential measurement value further comprises correcting the pressure differential measurement value with the calculated offset correction value. 
 
     
     
       18. The method of  claim 13 , wherein the gain correction value is calculated by dividing a difference in the first position pressure measurement signal and the second position pressure measurement signal by a difference in the first known reference pressure value and the second known reference pressure value. 
     
     
       19. The method of  claim 13 , wherein receiving the second known reference pressure value comprises calculating a second expected position-dependent pressure of the reference fluid disposed in an implanted fluid-filled device with the patient in the second position. 
     
     
       20. The method of  claim 13 , wherein the first and second position pressure measurement signals are voltages corresponding to the first and second pressure measurements acquired by the first pressure sensor with the patient in the first and second positions, respectively. 
     
     
       21. The method of  claim 13 , wherein the first and second known reference pressure values are known pressures.